The compounds of the formula I are the intermediates of pyrethroid type compounds with insecticidal action. The preparation of the active ingredients in the desired purity can only be carried out by using pure intermediates.
The compounds of the formula II are on one hand the characteristic by-products of the dienealkyldiazoacetate synthesis (Helv.Chim.Acta 7.390, 1924; J.Am.Chem.Soc. 66.395, 1944; Coll.Czech.Chem. Commun. 24.2240, 1959) widely used for the preparation of cyclopropane carboxylic acids of the formula I, on the other hand they are formed from the impurities present in the 1,1-dihalo-4-methyl-1,3-pentadiene used for the synthesis.
The amount of the contaminating esters can reach even 15 to 20% of the target product of formula I depending on the conditions (the effectivity of the catalyst, temperature etc.) of the synthesis and the purity of the diene.
The separation of the esters of general formula I and II by distillation is very difficult as their vapor pressure are very close to each other; therefore the different compounds distillate together. The chromatographic method for their separation (Synthesis 1960, 600) is wearisome and expensive on an industrial scale therefore has not been widespread.
The purification of the synthesis product can be carried out by removing the alkali sensitive contaminations, e.g. maleinic acid and fumaric acid esters, from the contaminated intermediate product by saponifying the product by adding alkaline solutions and transforming the said contaminations to water soluble salts (Hungarian Patent Application No. CI-1983).
A similar procedure can also be used when alcoholic medium is applied. According to the procedure the alcoholic solution of the permethrinic acid ester previously purified by distillation is treated with aqeous alkaline solution (European Patent No. 0034875).
The technical application of these methods is very difficult. In the course of the procedures a solvent (water or alcohol) and an aqeous alkaline hydroxide solution of great volume are used. The aqeous alcoholic phase formed in the course of the latter procedure also contains the dissolved endproduct. The recovery of the endproduct and the regeneration of the solvent demand further technological steps.